Summary Flight ABL814, an Air BC BAE146, serial number E2121, was cleared from Prince George, British Columbia, to Vancouver International airport at flight level 270 via J541 to BRYGE with a SKYPO Eight arrival. During the flight, the en route air traffic controller inadvertently cleared the aircraft to descend to an altitude that was below the minimum vectoring altitude (MVA) for the area. The MVA is the lowest altitude that meets obstruction clearance requirements in the specified airspace, and is the lowest altitude that Transport Canada has approved for vectoring of aircraft by air traffic control (ATC). The crew of ABL814 accepted the clearance and descended. By the time the controller recognized the problem, the aircraft had descended below radio coverage and could not be contacted directly using NAV CANADA's ground-based communications network. An aircraft in an adjacent control sector relayed the ATC instructions for ABL814 to climb. The crew of ABL814 received the relayed message, climbed to a safe altitude, and continued on to Vancouver. The weather was clear at the time of the incident, and the terrain was plainly visible to the crew; there was no risk of collision with the terrain. Ce rapport est galement disponible en franais. Other Factual Information The en route controller had just returned to the area control centre (ACC) operations room following a scheduled half-hour break and was working alone at the sector. Traffic in his sector was light; the controller had only ABL814 on his radar display. He had accepted an early handoff on that aircraft when it was about 20 nautical miles (nm) north of his sector, and he was monitoring its progress toward the Vancouver Terminal Area. Vancouver Terminal then informed the en route sector controller, who in turn informed ABL814, that there would be a flow delay of four minutes. The en route controller directed ABL814 to reduce speed from Mach 0.65 to Mach 0.62, and he monitored the aircraft's progress to confirm that the new speed would create the required delay. When the controller re-calculated the estimate, he determined that the aircraft was still going to be early. He then cleared ABL814 for the SKYPO Eight Arrival, to maintain 14 000 feet above sea level (asl) and 250 knots. His plan was to have the aircraft descend early and issue the speed restriction in order to reduce the aircraft's speed over the ground and thereby achieve the required delay; ABL814 descended in accordance with the clearance. The controller completed another calculation, which confirmed that the aircraft's lower speed at the lower altitude was resulting in an appropriate delay. The en route controller's radar display includes a number of maps and overlays. Of direct significance are two separate MVA lines that indicate the demarcation between different MVA areas within the controller's airspace. Both lines are similar in design, colour, orientation, and function to other lines on the display depicting MVA boundaries, but each represents a different altitude restriction; the north line marks the boundary of a 14 000-foot MVA, while the south line indicates the beginning of an 11 000-foot MVA. Under normal conditions, aircraft cleared for en route descents into Vancouver cross the north MVA line at an altitude between 16 000 and 17 000 feet asl. Similarly, aircraft tend to cross the south (second) MVA line at about 14 000 feet asl, at which time the controllers routinely issue further descent clearance to 11 000 feet asl. Controllers become accustomed to this standard descent profile, and there could develop a tendency to give the associated clearances as a matter of habit rather than as a cognitive action. There is no independent means for aircrew to cross-check MVA boundaries with published information available in the aircraft. As ABL814 approached the northern 14 000-foot MVA line, the en route controller informed the crew that he would have a lower altitude for them in five miles. Several minutes later, as the aircraft crossed into the 14 000-foot MVA area, the controller inadvertently cleared the crew to descend to 11 000 feet asl. The controller then began preparing for the next action associated with this aircraft; that action would be to pass control of the aircraft to the arrival controller. In preparation, he increased his visual scan on his radar display, away from the aircraft, and south of the MVA line, and immediately realized that he had descended the aircraft in error. ABL814 was descending through about 13 000 feet asl when the en route controller first attempted to clear the aircraft back up to 14 000 feet asl. However, by this time, the aircraft was below the communication coverage for the area and the pilot did not hear the transmission; he continued his descent and levelled off at 11 000 feet asl. The controller tried to contact the aircraft several times using transmitters located at both Kamloops and Vancouver but was unable to contact the crew from either site. The controller then moved to another en route controller's workstation and requested that controller to contact any aircraft in the vicinity in order to relay an instruction for ABL814 to make an immediate climb. Meanwhile, the crew of ABL814 had reported level at 11 000 feet asl on the ATC frequency but had not heard a response from the en route controller. The aircrew was familiar with this particular route and were aware that there were a number of dead zones in the communication coverage north of Vancouver. Their response was to continue inbound at 11 000 feet asl and to change their radio frequency to the Vancouver arrival frequency to request further direction. The Vancouver arrival controller heard the aircraft's transmissions on the arrival frequency, but he was unaware of the communication problems being addressed in the en route sector. Because ABL814 was outside arrival's airspace, the controller directed the aircraft to return to the previous en route frequency. ABL814 complied with that direction and eventually heard another pilot relay the instructions to climb. A direct controller-pilot communication (DCPC) is a two-way radio communication between a controlling air traffic control unit and an instrument flight rules (IFR) aircraft that is under its control, without resort to a relay through another unit. The ATC manual of operations (MANOPS) requires that, when a controller is unable to maintain two-way radio communication with an IFR aircraft, the controller take action to separate other aircraft from the aircraft having the communication failure and to attempt to regain communication. The specific procedures used by ATC are based on an underlying assumption that the aircraft crew will follow rules laid out in Canadian Aviation Regulations (CAR) and procedures described in the Canada Air Pilot and the Canada Flight Supplement (CFS). These procedures require that, if a communication failure occurs in visual meteorological conditions (VMC), the pilot shall continue the flight under visual flight rules (VFR) and land as soon as practicable. If the communication failure occurs under instrument flight conditions (IMC), while the pilot is being vectored at an altitude that is lower than a published IFR altitude, the pilot shall immediately climb to and maintain the appropriate minimum IFR altitude. In both cases, the procedures require the pilot to select the transponder to reply on Mode 3/A code 7600; this code is the internationally recognized signal that an aircraft is experiencing a communications failure and, when received by the NAV CANADA RAMP radar system, audio and visual warning are set off in the area control centre (ACC). In this occurrence, the aircraft was operating in VMC, and the pilot continued in visual conditions while attempting to re-establish communications on an alternative frequency. There is no clear definition for the term communication failure in applicable publications, and the pilot did not select code 7600. The ATC MANOPS also states that, as appropriate, the controller should inform adjacent ATC units of the details of a communication failure and request that all units attempt to contact the aircraft. At the time of this occurrence, the arrival controller, who handles an adjacent airspace, was physically separated from the en route controller's workstation and was not informed of the communication problem. The en route controller had chosen as his first action to advise another en route controller of the problem and request that an aircraft relay climb instructions to ABL814. Radar vectoring charts are developed for areas which require numerous minimum vectoring altitudes because of variable terrain features. These charts are designed to ensure that all the listed MVAs meet the obstacle clearance requirements of Transport Canada's publication TP 308 Criteria for the Development of Instrument Procedures. MVA charts do not require flight inspection certification, and TP 308 makes no direct mention of a specific requirement for communication capabilities either at or below the MVA. In the Vancouver area, the MVA charts are developed, monitored, and changed as necessary by NAV CANADA's Telecommunication Project Engineering Branch. This MVA chart design is based on the theoretical coverage of the available radar network; the altitudes on the charts are not flight-tested to validate this radar coverage. Additionally, the MVA charts do not take into account the area's actual or validated communication system coverage. CAR 602.124 defines the pilot's responsibility with respect to obstacles and terrain clearance during flight, and restricts a pilot from descending below certain published minimum altitudes except when on radar vectors. However, Vancouver ACC controllers routinely assigned an 11 000-foot altitude to inbound aircraft flying the SKYPO Eight Arrival; this altitude is based on an MVA chart for the area and is below the published minimum altitude for that route segment. Supervisory staff in the ACC indicated that it is an accepted local procedure to treat a standard instrument arrival as a vectoring procedure thereby allowing controllers to assign these lower altitudes which are based on the MVA charts. This procedure appears to be inconsistent with CAR 602.124, which specifically disallows a pilot from accepting these altitude assignments unless on a radar vector. Following this occurrence, Transport Canada indicated that, notwithstanding the direction of CAR 602.124, ATC may, once the aircraft is radar identified and under radar control, assign an MVA without specifically issuing a radar vector. This is accomplished with the clear understanding by ATC that the responsibility for obstacle clearance resides with ATC just as if ATC had issued a radar vector with the MVA assignment. Transport Canada recognizes that CAR 602.124 needs to be amended to reflect this operational application of assigning MVAs to an aircraft that is radar identified and under radar control and is taking action to change that regulation. Controllers and aircrew alike have noted that there are areas in the approaches to Vancouver where communication is temporarily lost because of blocking by high terrain. Local solutions to this problem have developed informally; controllers tend not to vector aircraft into areas where communications are known to be weak, and pilots tend to accept the temporary loss of communication as a routine and non-emergency situation. Pilots often find that, by waiting several minutes, or by changing to the next ATC sector's frequency, communications will be re-established. Controllers' expectations are based largely on their mental models of their sectors and the flow of traffic through this airspace. In general, an accurate mental model allows a controller to properly plan and manage the sector. Radar is the primary aid used to control traffic in this area, and all the relevant information presented on the radar display must be scanned continuously. As a controller's experience in a particular sector increases, the cues that are used to anticipate action become more subtle. In the en route sector, under normal traffic conditions and with a handoff in a customary position, the time that each aircraft remains on the controller's radar display is relatively constant, and the controller may tend to anticipate action based on the passage of time. Similarly, because an aircraft's descent profile is similar from day to day, some controllers may tend to perceive cues about the aircraft's horizontal progress from the aircraft's altitude read-out on the radar display. These relatively subtle cues tend to build into powerful mental models that will directly influence the controller's expectations. Minimum safe altitude warning (MSAW) systems were initially developed in 1976. These systems have the capability to warn an air traffic controller that an aircraft is either too close or is projected to be too close to terrain. MSAW systems alert the controller with both a visual and an aural alarm when an aircraft either penetrates or is predicted to penetrate a predetermined altitude. In the United States, MSAW service is provided for all aircraft operating under IFR and is provided when requested by aircraft operating under VFR. When a potentially unsafe condition is detected by an MSAW system, the controller alerts the flight crew. NAV CANADA has not yet implemented an MSAW system. All seven Canadian ACCs, including the Gander Oceanic Area Control Centre (OACC), the single stand-alone Terminal Control Unit facility at Ottawa, Ontario, and 23 control towers are equipped with systems that have the capacity to compute and display MSAW alerts; however, this capability is not yet implemented because the certification process and operational training for controllers are not complete. NAV CANADA has recently stated that the MSAW portion of the next software release was not included in the site test procedure scheduled for the spring of 1999. At the same time NAV CANADA, in its Corporate Safety Plan 1998/1999, continues to express the fact that it is committed to the national installation of Minimum Sector Altitude Warning Systems/Conflict Alert (MSAW/CA) on existing surveillance systems.